Pressure relief element, pressure relief device and battery

ABSTRACT

The present invention relates to a pressure relief element ( 11 ) to be used as an overpressure safety means in devices where a gaseous medium must be rapidly released in case of overpressure, wherein the pressure relief element ( 11 ) has at least one notch ( 9 ) which is designed as a predetermined breaking point where the pressure relief element ( 11 ) breaks at a certain level of overpressure, thereby irreversibly opening an exhaust path for the gaseous medium. The present invention also relates to a pressure relief device of an electrochemical battery, comprising such a pressure relief element and a battery comprising such a pressure relief device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/359,040, entitled “PRESSURE RELIEF ELEMENT, PRESSURE RELIEF DEVICEAND BATTERY,” filed May 16, 2014, which is a 35 U.S.C. § 371 Applicationof International Application No. PCT/EP2012/072851, entitled “PRESSURERELIEF ELEMENT, PRESSURE RELIEF DEVICE AND BATTERY,” filed Nov. 16,2012, and claims priority from and the benefit of U.S. ProvisionalApplication Ser. No. 61/560,646, entitled “VENTILATION FOR BATTERYSYSTEMS BY DINT OF A BURST MECHANISM,” filed Nov. 16, 2011, which arehereby incorporated by reference in their entirety for all purposes.

BACKGROUND

The present invention relates to a pressure relief element to be used asan overpressure safety means according to claim 1. The present inventionalso relates to a pressure relief device of an electrochemical batteryaccording to claim 12, comprising such a pressure relief element, and abattery according to claim 17, comprising such a pressure relief device.

SUMMARY

In several areas of technology there is a need for releasing anoverpressure of a gaseous medium in a rapid manner, like in the area ofpneumatic devices using compressed air or in the area of electrochemicalbatteries. Such batteries are increasingly used for hybrid and electricvehicles. Batteries for hybrid and electric vehicles need to allowpressure equalization in general, as in the case of an overload or shortcircuit large quantities of gas can be released. Even though in suchbattery systems normally a small cross-section is open anyway to allow acertain small air exchange during operation of the battery system, thesmall cross-section opening is not large enough for rapid gas release incases of emergency. The small opening provides a small air exchange andkeeps humidity inside and outside of the battery at the same level. Incase of a rapid major increase in pressure within the battery a safetymeans is required for avoiding an explosion of the battery housing.

It is an object of the invention to provide an overpressure safety meansfor devices where a gaseous medium must be rapidly released in case ofoverpressure which can be easily and cheaply manufactured and used in awide range of applications.

According to claim 1, the object of the invention is achieved by apressure relief element to be used as an overpressure safety means indevices where a gaseous medium must be rapidly released in case ofoverpressure, wherein the pressure relief element has at least one notchwhich is designed as a predetermined breaking point where the pressurerelief element breaks at a certain level of overpressure, therebyirreversibly opening an exhaust path for the gaseous medium. Theinvention has the advantage that a one-time usable element is proposedwhich comprises a predetermined breaking point where the pressure reliefelement breaks and then remains in an irreversible opened state. Suchpressure relief elements can be manufactured very cheaply and easily indifferent designs, both as an integrated pressure relief element whichis an integral part of a pressure relief device or as a separate partwhich can be mounted within a pressure relief device. In the lattercase, the pressure relief element can be an exchangeable part which canbe replaced after breaking in the course of a repair action. The notchis designed in a way that the pressure relief element breaks at apredefined level or range of overpressure, e.g. a range with an upperand a lower boundary level of overpressure.

The pressure relief element can be a gas-permeable element which alwaysallows a certain flow of gas, or it can be gas-tight before it breaks.

According to an advantageous embodiment of the invention the pressurerelief element can be formed as a plate-like and/or disc-like part. Insuch case, a pressure relief element is provided which has a flat, thinshape. The outer contour of the pressure relief element can have acircular shape, an oval shape, a rectangular or square shape or anyother shape suitable for the particular application.

Advantageously the pressure relief element can be made out of plasticmaterial. This allows to combine cheap manufacturing, in particular forthe mass production of pressure relief elements, with a determinablesafe design of the breaking point in form of the at least one notch. Inparticular, it is possible to manufacture large numbers of the pressurerelief element with current mass production technologies with a highrepeat accuracy of the level of overpressure upon which the breakingpoint reacts.

According to an advantageous embodiment of the invention

a) the pressure relief element comprises an injection side, the plasticmaterial being injected into an injection mould during the manufacturingof the pressure relief element from the injection side, and

b) the pressure relief element comprises a pressure side, which isarranged for being charged with the gaseous medium,

c) wherein the injection side and the pressure side are opposite sidesof the pressure relief element.

This allows for a reliable production of the pressure relief element outof plastic material with a high degree of fulfilment of specificationsand a high degree of repeat accuracy.

According to an advantageous embodiment of the invention the pressurerelief element comprises a profiled surface at least on one side in suchmanner that the material thickness of the pressure relief element islarger in the central area of the pressure relief element than in atleast one area surrounding the central area. If the pressure reliefelement is a flat, plate-like element, it is possible to design bothopposite sides of the pressure relief element with such a profiledsurface or only one side. In the latter case, the other side can bedesigned as a flat, planar surface. In case the pressure relief elementcomprises the aforementioned injection side and the pressure side, it isadvantageous to design the injection side as a side with such a profiledsurface. It is particularly advantageous to design the profiled surfacewith smooth transitions between the areas of different materialthicknesses. If this is realised on the injection side, the design ofthe pressure relief element supports the homogeneity of the plasticmaterial. In particular, turbulences in the material during theinjection process of the plastic material can be avoided. For example,it is advantageous to inject the plastic material from the central areaof the pressure relief element to the surrounding areas.

According to an advantageous embodiment of the invention the materialthickness of the pressure relief element can decrease in a decliningmanner from the central area towards the at least one area surroundingthe central area. This allows for a smooth transition between thethicker central area to the thinner surrounding area. By the decrease ofmaterial thickness in a declining manner the tension within the pressurerelief element can be controlled in such a way that the maximum tensionoccurs at the predetermined breaking point of the pressure reliefelement.

According to an advantageous embodiment of the invention the pressurerelief element comprises a circumferential area of increased materialthickness on its outer circumference. In this way, the pressure reliefelement can be designed with a more massive outer circumferential areawhich can be used for mounting and holding purposes, e. g. for holdingthe pressure relief element in a circular or else shaped holder device.

According to an advantageous embodiment of the invention the notch canbe located close to the circumferential area with increased materialthickness. Further, the notch can be shaped as a circumferential notchwhich surrounds the central area of the pressure relief elementcompletely or partially.

According to an advantageous embodiment of the invention the plasticmaterial of the pressure relief element can be a rigid plastic. Therigid plastic shall be selected from materials which are in their final,cured state relatively homogeneous and brittle or refractory.Advantageously a material is selected which has approximately the samebehaviour in a certain temperature range, e. g. in the temperature rangefrom −4o° C. to 85° C.

The material thickness of the pressure relief element in the area of thepredetermined breaking point can be a minimum thickness of e. g. 0.03mm. For applications of the pressure relief element for battery systemsfor hybrid and electric vehicles, advantageously the overpressure uponwhich the breaking point reacts ranges from 0.5 to 1 bar (aboveatmosphere pressure).

According to an advantageous embodiment of the invention the pressurerelief element can be a membrane, in particular a gas-permeablemembrane.

According to claim 12, the object of the invention is achieved by apressure relief device of an electrochemical battery, the pressurerelief device comprising at least one pressure relief element asdescribed herein before.

The pressure relief device can be designed in several ways, dependingupon the requirements of the particular application. For example, thepressure relief device can comprise an exhaust extension which extendsfrom the housing of the battery outwards, wherein the exhaust extensioncomprises at least one pressure relief element as described hereinbefore. The exhaust extension can be designed in the form of a pipe witha circular or other cross section. The pressure relief element can bemounted within the exhaust extension as a separate part or can be madeintegrally with the material of the exhaust extension.

According to an advantageous embodiment of the invention the pressurerelief device, in particular the exhaust extension, can comprise a tubeconnector for mounting a tube which allows constant pressureequalization between the interior and the exterior of the housing of thebattery. In such case the pressure relief device or its exhaustextension can fulfil more than one function, making it a multifunctionaldevice.

As a further function which can be realised by the pressure reliefdevice or in particular by the exhaust extension, it can shield thepressure relief element against the ambience of the housing of thebattery at least partly by means of a protection cap or maze. Theprotection cap or maze can particularly protect the pressure reliefelement against damage due to mechanical contacts or water/steam jet asused for vehicle cleaning. Also, the interior of the battery housing isprotected by the cap or maze.

According to an advantageous embodiment of the invention the pressurerelief device comprises a fixation element for fixing the exhaustextension to a housing wall of the housing of the battery in such mannerthat the exhaust extension is attached to the battery from the outsideof the housing of the battery by inserting the exhaust extension throughan opening in the housing wall of the housing of the battery and thenattaching the fixation element to the exhaust extension from the insideof the housing of the battery. This allows for an easy and quickmounting of the pressure relief device on a housing wall of the housingof the battery.

An advantageous method of attaching the pressure relief device to thehousing wall comprises the steps:

-   -   inserting the exhaust extension through an opening in the        housing wall of the housing of the battery,    -   attaching the fixation element to the exhaust extension from the        inside of 25 the housing of the battery.

According to claim 17, the object of the invention is achieved by abattery with a battery housing and a plurality of electrochemical cells,wherein the cells each comprise an own cell housing, wherein the cellsare located within the battery housing and wherein the battery housingcomprises a pressure relief device as described herein before.Particularly, cells with own degassing and/or pressure relief elementsintegrated in the cell housing may be used. In such case the inventionprovides for a common pressure relief path through the pressure reliefdevice for all cells mounted within the battery housing.

In a nutshell, the invention allows in the case of an increase ofpressure within the battery that a part opens at a predeterminedbreaking point and releases a large cross-section as a gas outlet.

This invention enables the rapid pressure equalization between thebattery and the environment when a cell releases a large amount of gasdue to overload, short circuit, etc. The opening at the battery issealed with a lid that has a notch. This notch serves as a predeterminedbreaking point. With increasing pressure, the breaking point cracks anda large cross-section gets open. The external area can be protected withadditional ribs or a maze against mechanical damage due to contact orwater/steam jet as used for vehicle cleaning. In addition, a small tubeconnector is provided which allows constant pressure equalizationbetween interior and external battery. The element should preferably bemade out of plastic - then with the hot gases the burst function will besupported by temperature. But it is also possible to use a metal part ora regular rupture disk of an external supplier in a kind of disccarrier. The design could also be a flange of any shape, which is boltedor clamped directly to the battery case or as shown at the images acylindrical part that is attached to a pipe piece.

DRAWINGS

The invention is now further described through exemplary embodiments andthrough drawings.

The drawings show:

FIG. 1 shows a battery with a plurality of electrochemical cells;

FIG. 2 shows a pressure relief device with integrated pressure reliefelement;

FIGS. 3-5 show another embodiment of a pressure relief device withintegrated pressure relief element;

FIGS. 6 and 7 show a pressure relief element; and

FIGS. 8 and 9 show another embodiment of a pressure relief device.

In the drawings, the same numerals refer to same elements.

DETAILED DESCRIPTION

FIG. 1 shows an electrochemical battery 1 comprising a battery housing 2and a plurality of electrochemical cells 3, which are located within thebattery housing 2. The electrochemical cells 3 comprise own cellhousings. The electrochemical cells 3 may be provided in the form ofprismatic or cylindrical cells or any other suitable cell format. Thehousing 2 can be designed, as depicted in FIG. 1, like a bin or a tray.For applications in vehicles the housing 2 is normally made of metalmaterial, but can also be made of lighter materials like resin or otherplastic materials.

On the outside of the housing 2 a pressure relief device 4 is mounted.The pressure relief device 4 comprises a tube-like exhaust extension 7which is fixed to the housing on a wall 6 of the housing 2. The exhaustextension 7 extends from the housing 2 of the battery 1 outwards andprovides for a breathing channel between the interior of the housing 2and the exterior, allowing air and moisture to exchange between theinterior and the exterior of the housing 2. Further, in case of anoverpressure within the housing 2, gases from the cells 3 could bereleased through the exhaust extension 7. The pressure relief device 4comprises a pressure relief element 11 which is mounted on the outsideof the exhaust extension 7. The pressure relief element 11 comprises anouter wall 8 which has a notch 9 which serves as a predeterminedbreaking point where the pressure relief element 11 breaks at a certainlevel of overpressure within the housing 2. The pressure relief device 4comprises a tube connector 10 for mounting the tube 5, as shown inFIG. 1. The tube connector 10 can be located at the end of the pressurerelief element 11 beyond the notch 9. As can be seen, the cross-sectionof the tube connector 10 as significantly smaller than the cross-sectionof the exhaust extension 7, which makes it necessary to provide thepredetermined breaking point for safety reasons.

In the FIGS. 3 to 5 another embodiment of a pressure relief device 4mounted to the housing wall 6 is depicted in different views. As can beseen, the pressure relief device 4 again comprises an exhaust extension7 in similar manner as shown in FIG. 2. On the exhaust extension 7 atube-like element with an outer wall 8 is mounted. On the outer wall 8 atube connector 10 is located. Within the outer wall 8 a pressure reliefdevice 11 in the form of a circular wall is located. The pressure reliefelement 11 again comprises a notch 9 as the predetermined breakingpoint. The notch 9 according to FIGS. 3 to 5 can be designed as acircular or semicircular groove, which completely or partially extendsalong the circumference of the pressure relief element 11.

In the embodiment of FIGS. 1 to 5 the pressure relief device 4 can bemade integrally of the same material, like plastic material. It is alsopossible to provide separate parts e.g. for the exhaust extension 7 andthe pressure relief element 11.

FIGS. 6 and 7 show an embodiment of a pressure relief element 11 as aseparate part, in particular as a disk-like part made out of plasticmaterial by an injection moulding process. FIG. 6 shows the pressurerelief element 11 in an isometric view, FIG. 7 shows a cross-sectionalview. As can be seen in the 30 figures, the pressure relief element 11comprises a generally flat lower side 69 and a profiled upper side 68which is the opposite side of the lower side 69. The upper side 68 is aninjection side of the pressure relief element 11, where the plasticmaterial is injected into an injection mould during the manufacturingprocess of the pressure relief element 11. The profiled injection side68 comprises a raised central area 60 with an increased materialthickness. The plastic material is injected in the area 60 into theinjection mould. Going from the central area 60 outwards, the materialthickness decreases through areas 61, 62 smoothly, e. g. in a decliningmanner, until an outer circular position 63 is reached. Going beyond theposition 63, the material thickness again increases in area 64 to form araised outer circular area 65 of the pressure relief element 11 whichcan serve as a mounting element for mounting the pressure relief elementin a pressure relief device. On the generally flat lower side 69, whichis the side of the pressure relief element 11 which is to be chargedwith a gaseous medium, a notch 9 in the form of a circular notch isprovided which acts as a predetermined breaking point of the pressurerelief element 11. The material 15 thickness in the area of the notch 9is e. g. only 0.03 mm.

FIGS. 8 and 9 show another embodiment of a pressure relief device 80composed of several separate parts which can be easily mounted to oneanother and to the housing wall 6. Further, the pressure relief device80 according to FIGS. 8 and 9 is suitable for incorporating a pressurerelief element 11 of FIGS. 6 and 7. FIG. 8 shows the completely mountedpressure relief device 80, FIG. 9 shows an explosional view of thepressure relief device 80.

The pressure relief device 80 of FIGS. 8 and 9 comprises a base part 83composed of different elements shown in FIG. 9. As can be seen in FIG.8, a protection cap 81 is mounted on the base part 83 by snap-hookelements 82. Further it can be seen that the base part 83 comprises atube connector 10.

Going to FIG. 9, it can be seen that the pressure relief device 80comprises 30 four separate parts plus a pressure relief element 11according to FIGS. 6 and 7. The four elements are the already describedprotection cap 81 and the base element 83 comprising of a pressurerelief element holder 90, a cap fixation part 91 and a fixation element92 for mounting the pressure relief device 80 to the housing wall 6. Forexplanation purposes, the pressure relief element holder 90 isadditionally shown in the left upper part of FIG. 9 from its bottomside.

The pressure relief device 80 according to FIGS. 8 and 9 can be mountedto the housing wall 6 of the housing 2 of the battery 1 in the followingway. First, the pressure relief element 11 is placed on a reception sideof the pressure relief element holder 90. Then the pressure reliefelement holder 90 with the pressure relief element 11 is placed withinthe cap fixation part 91 and then the protection cap 81 is fixed on thecap fixation part 91 by means of the snaphooks 82. In such way, thepressure relief element 11 is encapsulated between the pressure reliefelement holder 90 and the protection cap 81, while the pressure reliefelement holder 90 is encapsulated between the cap fixation part 91 andthe protection cap 81. The unit comprising of elements 11, 81, 90, 91can then be inserted through an opening in the housing wall 6 of thehousing 2. Then, the fixation element 92 is attached to a mechanicallink element 93 of the pressure relief element holder 90. The mechanicallink element 93 is designed to extend through the cap fixation part 91and the housing wall 6 to the inside of the housing 2. The mechanicallink 93 can be designed e. g. as a duff-tail link.

Those reviewing this disclosure will appreciate that various exemplaryembodiments have been shown and described, and that according to variousexemplary embodiments, features associated with one exemplary embodimentmay be used with features included in other exemplary embodiments.

As utilized herein, the terms “approximately,” “about,” “substantially,”and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” “connected,” and the like as used herein mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g., removableor releasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” etc.) are merely used to describe the orientation ofvarious elements in the FIGURES. It should be noted that the orientationof various elements may differ according to other exemplary embodiments,and that such variations are intended to be encompassed by the presentdisclosure.

It is important to note that the construction and arrangement of thebattery module having electrochemical cells with integrally formedterminals as shown in the various exemplary embodiments is illustrativeonly. Although only a few embodiments of the present inventions havebeen described in detail in this disclosure, those skilled in the artwho review this disclosure will readily appreciate that manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited in the claims.For example, the battery may be noncylindrical (e.g., oval, rectangular,etc.), the position of elements may be reversed or otherwise varied(e.g., orientation of terminals), and the battery could be a number ofdifferent of types (e.g., nickel metal hydride, lithium ion, lithiumpolymer, etc.). Accordingly, all such modifications are intended to beincluded within the scope of the present inventions. The order orsequence of any process or method steps may be varied or re-sequencedaccording to exemplary embodiments. Other substitutions, modifications,changes and omissions may be made in the design, operating conditionsand arrangement of the various exemplary embodiments without departingfrom the scope of the present invention.

The invention claimed is:
 1. A pressure relief disk of a battery module,comprising: a first side having a contoured surface; and a second side,opposite the first side, having a substantially flat surface portion, athickness of the pressure relief disk steadily decreasing from a raisedcentral portion to a base of a raised outer portion of the pressurerelief disk to define the contoured surface, the second side comprisinga notch that defines a predetermined breaking point between the raisedcentral portion and the raised outer portion of the pressure reliefdisk, the notch being disposed where the raised outer portion meets theremainder of the pressure relief disk.
 2. The pressure relief disk ofclaim 1, wherein the pressure relief disk is an injection moldedpressure relief disk.
 3. The pressure relief disk of claim 2, whereinthe first side is an injection side of the injection molded pressurerelief disk.
 4. The pressure relief disk of claim 1, wherein the notchis a circumferential notch that partially surrounds the raised centralportion of the pressure relief disk.
 5. The pressure relief disk ofclaim 1, wherein the notch is a circumferential notch that completelysurrounds the raised central portion of the pressure relief disk.
 6. Thepressure relief disk of claim 1, wherein the pressure relief disk has aminimum thickness at the notch.
 7. The pressure relief disk of claim 6,wherein the minimum thickness of the pressure relief disk at the notchis approximately 0.03 millimeters (mm).
 8. The pressure relief disk ofclaim 1, wherein the pressure relief disk has a maximum thickness in theraised outer portion of the pressure relief disk.
 9. The pressure reliefdisk of claim 1, wherein the first side is configured to be in fluidcommunication with an exterior of a housing of the battery module, andthe second side is configured to be in fluid communication with aninterior of the housing of the battery module.
 10. The pressure reliefdisk of claim 9, wherein the notch is configured to break at a certainlevel of overpressure of a gaseous medium in the interior of the housingof the battery module to irreversibly open an exhaust path such that thegaseous medium rapidly exits the interior of the housing of the batterymodule.
 11. The pressure relief disk of claim 1, wherein the notch isthe only predetermined breaking point of the pressure relief disk. 12.The pressure relief disk of claim 1, wherein the notch defines thepredetermined breaking point radially between the raised central portionand the raised outer portion of the pressure relief disk.
 13. A pressurerelief device of a battery module comprising a plastic pressure reliefdisk, the plastic pressure relief disk comprising: a first side having acontoured surface; and a second side, opposite the first side, having asubstantially flat surface portion, a thickness of the plastic pressurerelief disk steadily decreasing from a raised central portion to a baseof a raised outer portion of the plastic pressure relief disk to definethe contoured surface, the second side comprising a notch that defines apredetermined breaking point between the raised central portion and theraised outer portion of the plastic pressure relief disk, the raisedouter portion being engaged by a recess in a pressure relief disk holderof the pressure relief device.
 14. The pressure relief device of claim13, wherein the plastic pressure relief disk is an injection moldedplastic pressure relief disk, and wherein the first side is an injectionside of the injection molded plastic pressure relief disk.
 15. Thepressure relief device of claim 13, wherein the notch is the onlypredetermined breaking point of the plastic pressure relief disk, andwherein the notch is configured to break when an interior of a housingof the battery module reaches a predetermined pressure to irreversiblyopen an exhaust path to an exterior of the housing of the batterymodule.
 16. The pressure relief device of claim 13, wherein the plasticpressure relief disk has a minimum thickness at the notch and a maximumthickness in the raised outer portion of the plastic pressure reliefdisk.
 17. The pressure relief device of claim 13, wherein the plasticpressure relief disk demonstrates substantially similar properties overa temperature range between −40 degrees Celsius (° C.) and 85° C. 18.The pressure relief device of claim 13, wherein the plastic pressurerelief disk is substantially homogenous and is one of brittle of andrefractory.